This invention relates to a device for driving a drilling or percussion tool having a spindle that rotates with respect to a housing.
A device of this kind has been previously described in European patent application 84201720.4, upon which foreign priority is claimed by the applicant.
The present invention improves the means for converting the rotary motion of the drive shaft into an oscillatory motion of a drive member, and improves an associated elastic member, resulting in a design which is simple in construction, and a drilling or percussion tool which occupies less space and has a more favorable weight. One end of the spindle is adapted to fasten to a tool piece and the other end is connected to an oscillating percussion body movable in the housing by means of a guideway. A drive shaft rotates the tool spindle into rotation or actuates the percussion body via a transmission that is provided with means for converting the rotary motion of the drive shaft into an oscillatory motion of a drive member. The drive member is connected to the percussion body through an elastic member having a non-linear spring characteristic.
According to the invention the improved device is distinguished in that the drive member is mounted on the drive shaft or a shaft coupled therewith, which may take place at an angle deviating from 90 degrees to the center line thereof, and the elastic member is rotatably connected to the drive plate-like member, which is provided with a coupling means for engaging the percussion body.
Owing to the direct mounting of the drive member on the shaft associated therewith, the conversion mechanism can be made particularly simple and small. Moreover, the frequency of the oscillating motion can be boosted considerably, with retention of sufficient energy per stroke, which in some embodiments has a considerably better percussion effect on the intended workpiece.
In the preferred embodiment the coupling means is a tongue fastened to the plate which projects into an aperature arranged in the percussion body. In this embodiment the percussion body can be made small and is thereby suitable for high oscillation frequencies.
It can be advantageous to give the aperature a larger dimension in the direction of the stroke than the tongue of the elastic member, so that the desired non-linear spring characteristic is also obtained by using a plurality of stiff elastic members.
In another embodiment there is arranged extending along the elastic member a spring plate wherein the spring constant is less than that of the elastic member. Since the spring plate will be cushioned during the movement to a greater or lesser extent against the elastic member, a non-linear spring characteristic results.
If the drive member is mounted directly onto the motor shaft, it is preferable to provide the drive member on the motor side with a clutch, through which not only is assembly simplified, but the bending loads on that shaft will be reduced.
The invention further relates to a device which is provided with a percussion mechanism, for instance in the form described above, wherein the percussive force is transmitted directly to the tool piece to be coupled to the tool spindle. To that end the tool spindle is provided according to the invention with a tool-holding body, which is made with means for the rotation-proof fastening of a tool shank in the tool holder, which nonetheless permits an axial movement of the tool with respect to the drive shaft.
The above and other characteristics will be further elucidated in the detailed description below of a number of alternative embodiments.